1. Field of the Invention
This invention relates to the art of manufacturing and, more particularly, to a method and apparatus for controlling alignment of precision ground plates employed in a manufacturing process.
2. Description of Background
Most ceramic chip carriers employ green sheets that are combined into multiple layers to form a component substrate. In order to facilitate connections to conducting layers positioned between the multiple layers of green sheets, each layer or green sheet is punched with multiple holes or vias. Often times a green sheet will included upwards of 200,000 holes. In order to form the holes, the green sheet is positioned in a punch die tool. The punch die tool employs precision ground plates that align a punch and a die to form the hole. Conventional punch die tools employ upwards of 250 solenoid controlled punches that operate at 20 Hz, i.e., are activated 20 times a second, to form holes in the green sheet. The holes formed in the green sheet are typically between approximately 2.5 and 6 mils in diameter. Thus, alignment between the precision ground plates is critical to accurate hole placement. Even small temperature deviations between upper and lower plates can result in misaligned hole placement.
Conventionally, the precision ground plates are fabricated in a controlled environment of approximately 68° F. (20° C.). Equipment for measuring the plates is also kept in the same controlled environment. However, the equipment or tools used to form the holes in the plates, e.g., die punches etc., are not utilized in the same controlled environment. Punch tools usually operate in an ambient environment of about 72° F.-78° F. (22.22° C.-25.55° C.) while operating temperatures of the tools may range from about 72° F. to about 85° F. (22.22° C.-29.44° C.). Moreover, as the punches are controlled by individual solenoids, the operation of the tool results in a temperature variation between upper and lower plates. The variations in plate temperature result in improper hole placement. Variations in hole placement also result from a tool cooling down during a tool replacement cycle. When the variation in hole placement exceeds a limit value, the punch contacts or clips the die plate. At this point, the punch die tool must go off line, and the upper and lower plates are re-ground back to tolerance. This is a costly process, not only due to the cost associated with the actual repair, but with the punch die tool offline, production output drops for as long as the machine is offline.